1. Field of the Invention
The present invention pertains to a device and method for providing non-invasive intraoral electromuscular stimulation to a patient to treat a breathing disorder, such as obstructive sleep apnea, and, in particular, to a device and method wherein electromuscular stimulation is provided to the patient at a time prior to the onset of inspiration and continues through a major portion of the inspiratory phase and is applied at a level sufficient to induce muscle contraction without pain and/or is provided bilaterally at sublingual locations posterior to the frenulum in an anterior-to-posterior and/or posterior-to-anterior direction.
2. Description of the Related Art
Obstructive sleep apnea (OSA) is a medical condition in which the upper airway is repeatedly occluded during sleep despite continued respiratory effort. Those afflicted with OSA experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently during sleep with potentially severe degrees of oxyhemoglobin desaturation. An OSA sufferer typically experiences many apnea and/or hyponea events throughout the night. During an apnea event, the resulting hypoxia typically progresses until arousal occurs, which reestablishes airway patency.
Symptoms of OSA include snoring, choking and/or gasping during sleep, fragmented sleep, daytime sleepiness, fatigue and poor concentration. Airway obstruction can lead to a reduction in tidal volume, oxygen desaturation and progressive increases in respiratory rate. The long-term effects of OSA may be translated clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of OSA include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Hypersomnolent sleep apnea patients may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Studies of the mechanism of collapse of the airway suggest that during some stages of sleep, there is a general relaxation of the muscles that stabilize the upper airway segment. This general relaxation of the muscles is believed to be a factor contributing to OSA. More specifically, it is generally understood that the patency of the airway depends on the activity of the pharyngeal dilator muscles. Common sites of obstruction are behind the tongue and at the level of the soft palate. In a normal state, the muscles of the tongue, the genioglossus, hyoglossus, styloglossus, palatoglossus and the superior, inferior, transverse and vertical linguals, act to protrude or retract the tongue. Posterior fibers of the genioglossus draw the base of the tongue forward and anteriorly. One or more of these muscles normally contract reflexively during inspiration. However, it is generally understood that OSA suffers experience a reduction of lingual muscle activity during sleep as compared to nonapneics, thereby causing a reduction in airway patency.
Several therapeutic remedies exist for treating OSA. The most invasive, yet most likely to be successful, is a tracheotomy, which creates an airway bypass around the site of obstruction. Other surgical remedies include removal of deformed, loose or swollen structures or tissues in the upper airway. It is also known to apply positive air pressure at the mouth and/or nose of the patient to "splint" the airway, thereby maintaining an open passage to the lungs. In addition, pharmacological solutions have also been pursued.
None of these therapies is successful in all cases. Surgical relief is invasive, introduces a potential for surgical complications and is appropriate in only a small percentage of cases. On the other hand, the nasal or nasal/oral mask needed to apply a positive air pressure is not tolerated by some OSA patients. Pharmacological therapies have been, in general, less than satisfactory, and side effects are frequent.
It is also been proposed to treat OSA by electrically stimulating the musculature of the upper airway to prevent its relaxation and/or induce contraction, thereby preventing or minimizing subsequent blockage of the airway. There are two methods in which electromuscular stimulation can be applied to a patient; invasively or non-invasively. Invasive electrical stimulation of a muscle involves implanting one or more electrodes, either permanently or temporarily within the patient. These subcutaneous electrodes are typically located on or near the nerves that control the muscle to be stimulated. In some applications, the electrodes are placed in direct contact with the target muscle. Subcutaneous electrodes positioned adjacent the muscle or on or near the nerve controlling the muscle to be stimulated have the benefit of focusing the electrical energy on the muscle/nerve to be stimulated.
However, electrical muscle stimulation utilizing implanted electrodes requires surgical intervention, the permanent presence of foreign materials within the patient's tissue, and, in some applications, at least one electrical connection protruding from the patient. Consequently, there is a potential for infection or irritation at the surgical site and at the site where the electrode or electrical connection protrudes through the surface of the patient. In addition, it is reasonable to expect that some patients may be apprehensive about having a foreign object surgically placed within their body.
Non-invasive electrical stimulation of the muscles in the upper airway involves placing an electrode in direct contact with a surface of the patient and passing a current through the surface tissues adjacent the electrode. For example, U.S. Pat. No. 5,123,425 to Shannon et al. teaches applying an electrical stimulation to the exterior surface of the patient's neck below the chin to induce contraction of the upper airway muscles. In addition, U.S. Pat. No. 5,792,067 to Karell teaches an intraoral device that applies electrical stimulation to the hard palate, soft palate or pharyngeal area to induce contraction of the upper airway muscles. U.S. Pat. No. 5,190,053 to Meer teaches an intraoral device that applies electrical stimulation to the genioglossus muscle via electrodes located on the mucosa on the floor of the mouth on either side of the frenulum, which is the connecting membrane under the tongue that attaches the anterior portion of the tongue to the floor of the mouth.
While each of these non-invasive stimulation techniques claim to achieve some degree of success in opening the airway, it not clear that they are successful in a sufficient number of patients to render any one of these techniques a viable replacement to the other conventional treatments discussed above.
In addition to using either invasive or non-invasive stimulation on a patient, conventional electromuscular stimulation treatments typically initiate stimulation in one of two alternative timing methods. In a first timing method, stimulation is applied only when needed to counteract a detected breathing disorder, for example, at the onset of an apnea or when snoring is detected. This technique has the advantages of, for example, conserving energy and minimizing muscle fatigue. However, it is not clear that this stimulation timing method is sufficiently successful in breaking an apnea or stopping snoring in a significant number of OSA sufferers to be suitable for widescale and/or practical use.
According to a second timing method, stimulation is provided independent of the occurrence of a breathing disorder, such as an apnea, snore or other symptoms of respiratory distress. In this second method, stimulation is typically provided during each inhalation phase of a patient's breathing cycle and typically is initiated at the onset of inspiration. For example, U.S. Pat. Nos. 5,540,732 and 5,522,862 both to Testerman teach an invasive electrical stimulation system in which stimulation is applied to the patient in response to sensed inspiration. In an alternative method, such as that taught by U.S. Pat. No. 5,158,080 to Kallok, stimulation is provided at all times during the patient's breathing cycle, i.e., during the entire inspiratory phase and the entire expiratory phase. Although some success has been claimed when stimulation is provided independent of the occurrence of a breathing disorder, it not clear that the degree of success of either technique is sufficient to warrant the use such a timing technique on a widescale basis.
Other investigators, such as R. P. Schnall et al., as indicated, for example, in an article entitled "Dilatory Effects of Upper Airway Muscle Contraction Induced by Electrical Stimulation in Awake Humans", published in Volume 75 of the Journal of Applied Physiology in 1995, pages 1950-65, have experimented with various stimulation techniques, including the timing at which stimulation is initiated and the corresponding placement of the electrodes within the patient. However, as concluded in this article, the stimulation techniques attempted by Mr. Schnall et al. were unsuccessful in decreasing the number of breathing disorder events occurring in the test patients.